Heat a large skillet over medium-high heat. Add the ground lamb and onion, and use a wooden spoon to crumble the meat. Add the cumin, oregano, chile powder and salt, and continue to cook until meat is cooked through and onions are translucent.
Add the flour and garlic, and continue cooking until flour is toasty and garlic is fragrant, stirring often, for about 2 minutes. Gradually add the chicken broth, stirring briskly with a spoon to incorporate. Bring mixture to a boil, and then reduce heat to medium. Simmer mixture for about 15 minutes, or until slightly thickened. Remove from heat and stir in the black beans.
Prepare a 9x13 baking dish with nonstick spray. Ladle a small amount of the meat mixture into the bottom of the pan. Then, add the following layers in this order...
An even layer of 16 of the tortilla quarters
1/3 of the meat mixture
1/3 of the shredded cheese
Repeat these layers for a total of three times.
Bake at 350 for 30 minutes, or until cheese is slightly browned and bubbly. Allow casserole to sit for 10 minutes before serving.